Effect of current density on microstructure and mechanical property of Cu micro-cylinders electrodeposited in through silicon vias

In this paper, the through silicon via (TSV) blind holes with a diameter of 50 μm and a depth of 150 μm were prepared by MEMS micromachining technology. The Cu micro-cylinders (Cu-TSVs) were obtained by electrodepositing Cu in the blind holes using a direct current power. The mechanical properties of Cu-TSVs were measured using a self-made micro-compression system. The effect of current density on the mechanical property of Cu-TSVs was investigated. The experimental results indicated that when the current density increased from 1 mA/cm2 to 3 mA/cm2, the yield strength increased from 135.5 MPa to 177.6 MPa. However, when the current density further increased to 6 mA/cm2 and 9 mA/cm2, the yield strength decreased to 159.8 MPa and 119.3 MPa, respectively. Although it can improve the plating efficiency, the high current density led to the low yield strength. EBSD and XPS techniques were used to characterize the microstructure and impurities of Cu-TSVs. The grain size, grain boundary and grain orientation of Cu-TSVs electroplated at different current density were analyzed to discuss the mechanism.